The complement system is a part of the innate immune system which does not adapt to changes over the course of the host's life, but is recruited and used by the adaptive immune system. For example, it assists, or complements, the ability of antibodies and phagocytic cells to clear pathogens. This sophisticated regulatory pathway allows rapid reaction to pathogenic organisms while protecting host cells from destruction. Over thirty proteins and protein fragments make up the complement system. These proteins act through opsonization (enhancing phaogytosis of antigens), chemotaxis (attracting macrophages and neutrophils), cell lysis (rupturing membranes of foreign cells) and agglutination (clustering and binding of pathogens together).
The complement system has three pathways: classical, alternative and lectin. Complement factor D plays an early and central role in activation of the alternative pathway of the complement cascade. Activation of the alternative complement pathway is initiated by spontaneous hydrolysis of a thioester bond within C3 to produce C3(H2O), which associates with factor B to form the C3(H2O)B complex. Complement factor D acts to cleave factor B within the C3(H2O)B complex to form Ba and Bb. The Bb fragment remains associated with C3(H2O) to form the alternative pathway C3 convertase C3(H2O)Bb. Additionally, C3b generated by any of the C3 convertases also associates with factor B to form C3bB, which factor D cleaves to generate the later stage alternative pathway C3 convertase C3bBb. This latter form of the alternative pathway C3 convertase may provide important downstream amplification within all three of the defined complement pathways, leading ultimately to the recruitment and assembly of additional factors in the complement cascade pathway, including the cleavage of C5 to C5a and C5b. C5b acts in the assembly of factors C6, C7, C8, and C9 into the membrane attack complex, which can destroy pathogenic cells by lysing the cell.
The dysfunction of or excessive activation of complement has been linked to certain autoimmune, inflammatory, and neurodegenerative diseases, as well as ischemia-reperfusion injury and cancer. For example, activation of the alternative pathway of the complement cascade contributes to the production of C3a and C5a, both potent anaphylatoxins, which also have roles in a number of inflammatory disorders. Therefore, in some instances, it is desirable to decrease the response of the complement pathway, including the alternative complement pathway. Some examples of disorders mediated by the complement pathway include age-related macular degeneration (AMD), paroxysmal nocturnal hemoglobinuria (PNH), multiple sclerosis, and rheumatoid arthritis.
Age-related macular degeneration (AMD) is a leading cause of vision loss in industrialized countries. Based on a number of genetic studies, there is evidence of the link between the complement cascade and macular degeneration. Individuals with mutations in the gene encoding complement factor H have a fivefold increased risk of macular degeneration and individuals with mutations in other complement factor genes also have an increased risk of AMD. Individuals with mutant factor H also have increased levels of C-reactive protein, a marker of inflammation. Without adequate functioning factor H, the alternative pathway of the complement cascade is overly activated leading to cellular damage. Inhibition of the alternative pathway is thus desired.
Paroxysmal nocturnal hemoglobinuria (PNH) is a non-malignant, hematological disorder characterized by the expansion of hematopoietic stem cells and progeny mature blood cells which are deficient in some surface proteins. PNH erythrocytes are not capable of modulating their surface complement activation, which leads to the typical hallmark of PNH—the chronic activation of complement mediated intravascular anemia. Currently, only one product, the anti-C5 monoclonal antibody eculizumab, has been approved in the U.S. for treatment of PNH. However, many of the patients treated with eculizumab remain anemic, and many patients continue to require blood transfusions. In addition, treatment with eculizumab requires life-long intravenous injections. Thus, there is an unmet need to develop novel inhibitors of the complement pathway.
Factor D is an attractive target for inhibition or regulation of the complement cascade due to its early and essential role in the alternative complement pathway, and its potential role in signal amplification within the classical and lectin complement pathways. Inhibition of factor D effectively interrupts the pathway and attenuates the formation of the membrane attack complex.
While initial attempts have been made to develop inhibitors of factor D, there are currently no small molecule factor D inhibitors in clinical trials. Examples of factor D inhibitors or prolyl compounds are described in the following disclosures.
Biocryst Pharmaceuticals U.S. Pat. No. 6,653,340 titled “Compounds useful in the complement, coagulat and kallikrein pathways and method for their preparation” describes fused bicyclic ring compounds that are potent inhibitors of factor D. Development of the factor D inhibitor BCX 1470 was discontinued due to lack of specificity and short half-life of the compound. Novartis PCT patent publication WO2012/093101 titled “Indole compounds or analogues thereof useful for the treatment of age-related macular degeneration” describes certain factor D inhibitors. Novartis PCT patent publications WO2014/002057 titled “Pyrrolidine derivatives and their use as complement pathway modulators” and WO2014/009833 titled “Complement pathway modulators and uses thereof” describe additional factor D inhibitors with heterocyclic substituents. Additional factor D inhibitors are described in Novartis PCT patent publications WO2014/002051, WO2014/002052, WO2014/002053, WO2014/002054, WO2014/002058, WO2014/002059, and WO2014/005150.
Bristol-Myers Squibb PCT patent publication WO2004/045518 titled “Open chain prolyl urea-related modulators of androgen receptor function” describes open chain prolyl urea and thiourea related compounds for the treatment of androgen receptor-associated conditions, such as age-related diseases, for example, sarcopenia.
Japan Tobacco Inc. PCT patent publication WO1999/048492 titled “Amide derivatives and nociceptin antagonists” describes compounds with a proline-like core and aromatic substituents connected to the proline core through amide linkages useful for the treatment of pain.
Ferring B. V. and Yamanouchi Pharmaceutical Co. lTD. PCT patent publication WO1993/020099 titled “CCK and/or gastrin receptor ligands” describes compounds with a proline-like core and heterocyclic substituents connected to the proline core through amide linkages for the treatment of, for example, gastric disorders or pain.
Alexion Pharmaceuticals PCT patent publication WO1995/029697 titled “Methods and compositions for the treatment of glomerulonephritis and other inflammatory diseases” discloses antibodies directed to C5 of the complement pathway for the treatment of glomerulonephritis and inflammatory conditions involving pathologic activation of the complement system. Alexion Pharmaceutical's anti-C5 antibody eculizumab (Soliris®) is currently the only complement-specific antibody on the market, and is the first and only approved treatment for paroxysmal nocturnal hemoglobinuria (PNH).
Compounds which mediate the complement pathway, and for example, act as factor D inhibitors are needed for treatment of disorders in a host, including a human, associated with misregulation of the complement cascade.